Chewing gum typically comprises two major portions, namely a chewable portion such as a gum base and a non-chewable portion including sweetening agents, softening agents, flavoring agents, and the like. The gum base is a masticatory substance, which is insoluble in the saliva, comprising a blend of natural and/or synthetic rubbers, natural and/or synthetic resins, fillers, plasticizers, emulsifiers, waxes, and the like. On the other hand, the non-chewable portion includes substances which are readily soluble and mostly dissolve out into the mouth upon chewing.
Since the gum base is not dissolved by saliva, it remains as it is for a long period of time when chewing gum is discarded in an environment such as on the street after being chewed, thus causing a pollution problem. A method of replacing ingredients in the gum base with disintegratable or biodegradable ingredients has been proposed as one way to reduce such an impact of chewing gum onto the environment.
Japanese Patent Application Laid-open No. H6-7090 suggests that a gum base which is susceptible to biodegradation can be obtained by replacing a paraffin component, which is used as a wax in a gum base, with a triglyceride composition having a specific fatty acid composition. However, this gum base cannot provide a fundamental solution to the pollution problem since it also contains non-degradable components other than the wax, in particular synthetic elastomers, which remain in the environment.
In imparting disintegratability and biodegradability to a gumbase, there rises a problem that non-degradable synthetic rubbers and resins, in particular butyl rubber and polyvinyl acetate are used. They are used as a major component of the gum base because of their durability and convenience. This problem has been solved by using a natural rubber in place of butyl rubber; however, replacement of polyvinyl acetate is not easy in terms of texture and processibility. Accordingly, in order to impart disintegratability and biodegradability to a gum base, there is a need for a material which has a function comparable to that of polyvinyl acetate and at the same time is disintegratable or biodegradable.
Japanese Patent Application Laid-open No. H8-196214 discloses that a biodegradable chewing gum can be obtained by using a biodegradable polymer comprising polyesters or polycarbonates in a gum base. In this way, biodegradability can be imparted to the entire gum base. However, since the glass transition temperature of this gum base is at the highest 37° C., a gum base with a soft chewing texture only can be obtained.
Further, Japanese Patent Application Laid-open No. H10-262566 discloses a biodegradable chewing gum, in which a faction mainly comprising glutenin fractionated from wheat gluten is heat-treated and blended. However, the amount of said treated glutenin to be added is limited to less than 8% since its addition creates insufficient chewing texture; thus it is impossible to entirely replace other non-biodegradable gum base ingredients.
On the other hand, International Publication No. WO 00/19837 discloses a technology to apply a lactic acid polymer to a gum base as a biodegradable polymer. In this publication, in order to obtain soft chewing texture, D-lactic acid monomers are further added to apoly (D-, L-lactic acid) polymer and their co-polymer with glycolic acid to reduce a crystallinity and to lower a glass transition temperature and then a plasticizer such as triacetin is further added for further softening. However, since the glass transition temperature of the polymer itself is lowered, the chewing texture deteriorates when being chewed for a long time, and processibility is reduced. Further, sufficient disintegratability may not be obtained since the crystallinity is reduced.